The present invention relates to gas generant compositions that upon combustion produce a relatively smaller amount of solids and a relatively abundant amount of gas. It is an ongoing challenge to reduce the amount of solids and increase the amount of gas thereby decreasing the filtration requirements for an inflator. As a result, the filter may be either reduced in size or eliminated altogether thereby reducing the weight and/or size of the inflator. Additionally, reduction of combustion solids provides relatively greater amounts of gaseous products per gram or unit of gas generating composition. Accordingly, less gas generant is required when greater mols of gas are produced per gram of gas generant. The result is typically a smaller and less expensive inflator due to reduced manufacturing complexity.
Yet another concern is that the compositions must exhibit burn rates that are satisfactory with regard to use in vehicle occupant protection systems. In particular, compositions containing phase stabilized ammonium nitrate may exhibit relatively lower burn rates requiring various measures to improve the burn rate. Accordingly, the development of energetic fuels is one ongoing research emphasis whereby the less aggressive burn characteristics of preferred oxidizers such as phase stabilized ammonium nitrate are compensated.
Another concern is that many types of fuels form thermally unstable compositions when combined with phase stabilized ammonium nitrate. The use of phase stabilized ammonium nitrate (PSAN) is desirable because it contributes to relatively greater amounts of gas produced per gram of gas generant. However, the composition incorporating PSAN must be thermally stable and pass U.S. Car Aging Requirements. Stated another way, the composition must remain reliable with regard to performance even after being aged at 107 degrees Celsius for 400 hours.
Tetrazoles and derivatives of tetrazoles are desirable as fuels, given that they have high nitrogen and high energy as compared to other non-azide fuels. 5-aminotetrazole (5-AT) is one fuel that is preferred because of its energetic nature. Nevertheless, the presence of certain functional groups (such as primary amines, hydroxylamines, and alcohols) on the tetrazole moiety complicates its use as a fuel in a gas generant composition. Furthermore, compositions containing 5-AT are not thermally stable when combined with PSAN. It is believed that the prevalence of an acid-base reaction of the primary amines with the strong acid in such tetrazole/PSAN compositions forms a low-melting point eutectic mixture, thereby making these types of compositions less desirable as a gas generant composition.